1. Field of the Invention
The present invention relates to a disc-chucking mechanism which attaches and detaches a disc in a hard disk device, a servo writer, a media tester, a head tester, etc.
2. Description of the Related Art
A typical disc for use in a hard disk device is driven with a spindle motor. The disc is produced by polishing a blank material of aluminum or glass to obtain a precisely flat surface and applying a metal material on the flat surface. The disc has an extremely small thickness relative to the flatness thereof and is very easily distorted.
Therefore, it is difficult to attach the disc to the spindle motor without degrading the flatness of the disc. In addition, when the disc is used in the servo writer, the media tester, or the like and must be attached and detached frequently, it is necessary to hold the disc in a short time with high reliability.
FIG. 8 is a diagram showing the construction of a known chucking mechanism. When a disc D is fitted to a central portion 1a of a cylindrical center shaft 1, a high-precision parallel spacer 2 is disposed around the central portion 1a and the disc D is placed on the parallel spacer 2. Then, a cap 3 is placed on the top surface of the disc D and is fastened to the central portion 1a with a washer 4 and a screw 5. When the screw 5 is attached, a torque driver or the like must be used to prevent the disc D from distorting. Thus, there is a disadvantage in that the attaching/detaching process requires a long time.
In addition, as shown in FIG. 9, instead of using the screw 5, a disc D may also be attached by vacuum suction using a suction hole 1b formed in a center shaft 1. However, since a cap 3 is provided as a separate component, a conveying mechanism for the cap 3 is required when automation for mass production is to be achieved. Accordingly, this structure is not suitable in view of space saving and cost reduction.
In addition, as shown in FIG. 10, a disc D may also be attached/detached by moving three lugs 6 provided on a central portion 1a with respect to an inner circumferential portion of the disc D in the radial direction thereof. In this method, a separate component like the above-mentioned cap 3 or the like is not required. However, since the disc D is held using small regions where the three lugs 6 come into contact with the disc D, stress concentration occurs at these regions and the disc D is easily distorted. Therefore, it is difficult to maintain the high flatness of the disc D.
In the above-described known structures, a mechanism which quickly and reliably attaches/detaches the disc with high precision and small distortion is not established, although such a mechanism is important.